1. Field of the Invention
The present invention relates to a method of etching a magnetic material film and a method of manufacturing a thin-film magnetic head that has at least an induction-type electromagnetic transducer.
2. Description of the Related Art
Recent years have seen significant improvements in the areal recording density of hard disk drives. In particular, areal recording densities of latest hard disk drives reach 80 to 120 Gbit/(inch)2 and are even on a pace to exceed that level. Thin-film magnetic heads are required of improved performance accordingly.
Among the thin-film magnetic heads, widely used are composite thin-film magnetic heads made of a layered structure including a recording head having an induction-type electromagnetic transducer for writing and a reproducing head having a magnetoresistive element (that may be hereinafter called an MR element) for reading.
In general, a recording head incorporates: a medium facing surface (air bearing surface) that faces toward a recording medium; a bottom pole layer and a top pole layer that are magnetically coupled to each other and include magnetic pole portions opposed to each other and located in regions of the pole layers on a side of the medium facing surface; a recording gap layer provided between the magnetic pole portions of the top and bottom pole layers; and a thin-film coil at least part of which is disposed between the top and bottom pole layers and insulated from the top and bottom pole layers.
Higher track densities on a recording medium are essential to enhancing the recording density among the performances of a recording head. To achieve this, it is required to implement a recording head of a narrow track structure in which the track width, that is, the width of the two magnetic pole portions opposed to each other on a side of the medium facing surface, with the recording gap layer disposed in between, is reduced down to microns or the order of submicron. Semiconductor process techniques are utilized to achieve such a structure.
With decreasing track width, it becomes harder to generate a high-density magnetic flux between the two magnetic pole portions that are opposed to each other with the recording gap layer in between. On that account, it is desirable that the magnetic pole portions be made of a magnetic material having a higher saturation flux density.
Typical high saturation flux density materials include NiFe and CoNiFe which are formable into films by plating, and FeN, FeCo, and CoFeN which have still higher saturation flux densities and are formable into films by sputtering.
To form a magnetic layer including a magnetic pole portion using a high saturation flux density material that is formable into a film by sputtering, the following method has been conventionally used. That is, in this method, a film of the high saturation flux density material is initially formed by sputtering. Then, a mask made of a photoresist is formed on this film. The film is then selectively etched by ion beam etching, thereby patterning the film to form the magnetic layer. In this method, however, it has been difficult for a magnetic pole portion of 0.5 μm or less in width to be formed with high precision due to low etching rates of the ion beam etching and heavy erosion of the mask.
When a high saturation flux density material that is formable into a film by plating is used to form a magnetic layer as mentioned above, a magnetic layer including a magnetic pole portion of 0.5 to 0.6 μm or so in width can be formed by employing a selective plating method such as frame plating. For example, among the high saturation flux density materials that are formable into films by plating, NiFe having a higher Fe composition ratio can provide saturation flux densities of 1.5 to 1.6 T (tesla) and allow relatively stable control on composition. With CoNiFe, saturation flux densities around 1.8 T are attainable.
When the areal recording densities reach 80 to 120 Gbit/(inch)2, however, track widths on the order of 0.1 to 0.2 μm are required. Such small track widths require that the magnetic pole portion be rendered around 4 to 5 μm in thickness so that a magnetic flux passing through the magnetic layer is prevented from being saturated before it reaches the medium facing surface. Nevertheless, it is extremely difficult to form a magnetic pole portion having a width on the order of 0.1 to 0.2 μm and a thickness on the order of 4 to 5 μm by plating. Hence, one may employ the following method to form the magnetic pole portion. That is, in the method, a magnetic pole portion having a width on the order of 0.5 to 0.6 μm and a thickness on the order of 4 to 5 μm is initially formed by plating. Then, the sidewalls of the magnetic pole portion are etched by ion beam etching, for example, so that the width of the magnetic pole portion is reduced to be on the order of 0.1 to 0.2 μm.
Reference is now made to FIGS. 57A to 61A and FIGS. 57B to 61B to describe an example of a method of manufacturing a thin-film magnetic head of related art, in which the magnetic pole portion is formed by the above-described method. FIGS. 57A to 61A are cross sections each orthogonal to the air bearing surface and the top surface of the substrate. FIGS. 57B to 61B are cross sections of the magnetic pole portion each parallel to the air bearing surface. According to the manufacturing method, as shown in FIGS. 57A and 57B, an insulating layer 102 made of alumina (Al2O3), for example, is deposited to a thickness of about 1 to 2 μm on a substrate 101 made of aluminum oxide and titanium carbide (Al2O3—TiC), for example. Next, on the insulating layer 102, a bottom shield layer 103 made of a magnetic material such as Permalloy is formed for a reproducing head. On the bottom shield layer 103, a bottom shield gap film 104 as an insulating film is formed to a thickness of 10 to 25 nm, for example.
On the bottom shield gap film 104, an MR element 105 for magnetic signal detection is formed to a thickness of tens of nanometers. Next, although not shown, a pair of electrode layers are formed to a thickness of tens of nanometers to be electrically connected to the MR element 105 on the bottom shield gap film 104. Next, a top shield gap film 107 as an insulating film is formed to a thickness of 10 to 25 nm, for example, on the bottom shield gap film 104 and the MR element 105. The MR element 105 is embedded in the shield gap films 104 and 107.
Next, on the top shield gap film 107, a top shield layer 108 of a magnetic material is formed to a thickness of about 3 μm. On the top shield layer 108, an insulating layer 109 made of alumina, for example, is formed to thickness of 0.2 μm, for example, for separating the recording head and the reproducing head from each other. Next, a bottom pole layer 110 is formed to a thickness of 1.5 to 2.0 μm, for example, on the insulating layer 109.
Next, as shown in FIGS. 58A and 58B, a recording gap layer 111 of an insulating material such as alumina is formed on the bottom pole layer 110 to a thickness of 100 nm, for example. Then, a contact hole is formed in the recording gap layer 111 at a position where the bottom pole layer 110 and a top pole layer to be described later are coupled to each other.
Next, although not shown, a thin magnetic film of, e.g., FeCo that is a high saturation flux density material, is formed by sputtering over the entire surface. On the magnetic film, a pole portion layer 112a and a coupling layer 112b of the top pole layer 112 are formed to a thickness of 4 to 5 μm by frame plating. The pole portion layer 112a is located near an air bearing surface to be described later. The pole portion layer 112a defines the recording track width. The coupling layer 112b is located in the position of the contact hole, and is connected to the bottom pole layer 110. At this stage, the pole portion layer 112a has a width of 0.5 to 0.6 μm.
Next, as shown in FIGS. 59A and 59B, sidewalls of the pole portion layer 112a are etched by ion beam etching so as to make the width of the pole portion layer 112a 0.1 to 0.2 μm or so. Furthermore, through this ion beam etching, the magnetic film, the recording gap layer 111 and the bottom pole layer 110 are also etched using the pole portion layer 112a and the coupling layer 112b as masks. This forms a trim structure in which the sidewalls of the magnetic pole portion of the top pole layer 112, the recording gap layer 111 and part of the bottom pole layer 110 are formed vertically in a self-aligned manner. Furthermore, the bottom pole layer 110 is provided with a recess to place a thin-film coil in.
Next, as shown in FIGS. 60A and 60B, an insulating film 113 made of alumina, for example, is formed over the entire surface. A thin-film coil 114 made of Cu, for example, is then formed to a thickness of 1.5 μm, for example, by frame plating on the insulating film 113 inside the above-mentioned recess. In FIG. 60A, the reference numeral 114a represents a connecting portion of the thin-film coil 114 to be connected to a lead layer described later.
Next, as shown in FIGS. 61A and 61B, a thick insulating layer 115 of alumina, for example, is formed over the entire surface, and then the top surface of the insulating layer 115 is flattened so that the pole portion layer 112a and the coupling layer 112b are exposed. Then, a portion of the insulating layer 115 lying over the connecting portion 114a of the thin-film coil 114 is removed by etching, so that the connecting portion 114a is exposed. On the surface thus flattened, a yoke portion layer 112c of the top pole layer 112 is formed so as to couple the pole portion layer 112a and the coupling layer 112b to each other. Here, the lead layer 116 is simultaneously formed to be connected to the connecting portion 114a. The yoke portion layer 112c is made of a magnetic material for making the recording head, such as Permalloy. Next, an overcoat layer 117 made of alumina, for example, is formed over the entire surface. The surface is then flattened and not-shown electrode pads are formed thereon. Finally, lapping of the slider including the foregoing layers is performed to form the air bearing surface 130 of the recording and reproducing heads. The thin-film magnetic head is thereby completed.
FIG. 62 is an explanatory diagram showing the cross section of the thin-film magnetic head shown in FIG. 61A in association with a plan view of the thin-film magnetic head in which the overcoat layer 117 and the yoke portion layer 112c are omitted.
In the manufacturing method illustrated in FIGS. 57A to 61A and FIGS. 57B to 61B, the sidewalls of the pole portion layer 112a are etched by ion beam etching as shown in FIG. 59B, so that the pole portion layer 112a is reduced in width. This can cause the following problems of the above-described manufacturing method.
A first problem is that the ion beam etching might reduce the pole portion layer 112a in thickness from an initial thickness of 4-5 μm to a thickness on the order of 1.5-2.0 μm. When the pole portion layer 112a becomes thus smaller in thickness, a magnetic flux passing through the top pole layer 112 is saturated before it reaches the air bearing surface 130, which makes it impossible to attain a sufficient overwrite property. To avoid this, it is conceivable that the initial thickness of the pole portion layer 112a could be made greater than 4 to 5 μm. For that purpose, however, the frame for forming the pole portion layer 112a must also be made greater in thickness, which makes it difficult to form the frame with high precision.
A second problem is that the above-described manufacturing method requires quite long time to etch the sidewalls of the pole portion layer 112a by the ion beam etching.
A third problem is that, because the above-described manufacturing method consumes quite long time to etch the sidewalls of the pole portion layer 112a, a portion of the pole portion layer 112a located near the top surface thereof may get thinner than a portion located near the recording gap layer 111, as shown in FIG. 59B. Consequently, the pole portion layer 112a tends to decrease in thickness, and the magnetic flux tends to become saturated near the interface between the pole portion layer 112a and the yoke portion layer 112c. In either case, the overwrite property deteriorates.
As a fourth problem, since the above-mentioned manufacturing method heavily etches the sidewalls of the pole portion layer 112a, the recording track width can vary greatly among a plurality of thin-film magnetic heads formed on one wafer and among different wafers, resulting in poor yields of the thin-film magnetic heads.
Meanwhile, even if the manufacturing method shown in FIGS. 57A to 61A and FIGS. 57B to 61B is used, the pole portion layer 112a can only attain saturation flux densities around 1.8 T at best, because the pole portion layer 112a must be made of a material that is formable by plating.
When the areal recording density reaches 80 to 120 Gbit/(inch)2 and a track width of around 0.1 to 0.2 μm is demanded, the magnetic pole portion must be made of a material having a saturation flux density of around 2.0 to 2.4 T. In that case, the magnetic pole portion can no longer be formed by plating.
Thus, it has been difficult to manufacture a thin-film magnetic head having a small recording track width on the order of 0.1 to 0.2 μm while attaining a sufficient overwrite property.